当前大气气溶胶的成分比较复杂，其水溶性离子成分影响着大气质量，并且对人类健康不利。因此，对水溶性离子成分进行快速可靠的检测是环境科学领域中的一项重要研究工作。以SO2－4为例，研究采用傅里叶变换红外光谱(FTIR)技术，对水溶性气溶胶离子的消光系数进行测量，并通过理论分析计算得到其复折射率N的过程。通过测量大气气溶胶水溶性SO2－4离子的质量消光截面k和消光系数α，再根据消光系数α来计算复折射率N的虚部ni，使用KK（Kramers-Kronig）关系，来计算复折射率N的实部nr，并对实验结果进行了分析和讨论。

Studies indicate that current composition of atmospheric aerosol is complex, and its water-soluble ions affect air quality. The ions can produce significant negative effect on the human health. Therefore, rapid and reliable detection of water-soluble ion is an important research work in environmental science. Take SO2－4 ion as an example, the extinction coefficient of water-soluble aerosol is measured by Fourier transform infrared spectroscopy (FTIR) technology, and the complex refractive index N is also calculated through theoretical analysis. By measuring the mass extinction cross section k and extinction coefficient α of the atmospheric aerosol water-soluble ion, the imaginary part ni of the complex refractive index N is calculated according to the extinction coefficient α and the real part nr of the complex refractive index N is also calculated by using the KK (Kramers-Kronig) relationship. The experimental results are also analyzed and discussed.